Up until now, we have modeled random variables with a probability mass function or a probability density function.  We then discussed in detail the theory behind inference on the unknown parameters.  But in many situations, there are other variables that play a role in the behavior of the variable we're interested in modeling. Analysis of variance (ANOVA) is one of the most widely used statistical techniques.  The basic idea underlying ANOVA is the partitioning of variability.  By partitioning variability, ANOVA is a set of inferential methods for investigating the differences in the means of multiple populations or treatments.  The specific ANOVA method we will study is oneway ANOVA.